Oxygen Segregation Energetics and Tensile Plasticity of Aluminum Grain Boundaries

Abstract

Grain boundary (GB) oxidation plays an important role in determining the chemical and mechanical properties of metals, while its associated structural evolution and deformation mechanisms at the atomic scale are still not fully understood. In this work, we employ reactive molecular dynamics simulations to investigate the tensile behavior of four aluminum tilt-symmetric oxygen-loaded bigrain GBs containing structure units (SUs) “C/D” and “E”. We find that there is a critical oxygen density that controls changes in oxygen-loaded GB structure, as well as the tensile behavior and deformation mechanisms. Below such a critical density, GB tensile yield stress increases because the presence of oxygen hinders dislocation nucleation from SU “E”, but decreases because oxygen favors the phase transformation of GBs with SU “C/D”. Above such a critical density, a dense oxide layer is formed and the dislocation nucleates from the GB oxide layer–grain interface. Whether the dislocation is easy or hard to nucleate is dependent on the mismatch between the amorphous GB oxide layer and the grain because the mismatch is determined by the geometrical orientation of the grain adjacent to the amorphous GB oxide layer. Particularly, the hardening phenomenon seen in the unoxidized GB with SUs “E” may vanish as the GB oxidation deepens because oxygen changes the behavior of dislocation nucleation from SUs “E”. The findings of this study may shed light on the oxidation-modulated behavior and deformation mechanism of metal GBs.